Where can I buy a pair of wearable transmitter and receiver so that when a button is pushed on the transmitter, the receiver will beep and/or vibrate? This is for a doctor friend who wants to page her nurse in urgent situation when the nurse is in some adjacent room. The nurse is to go find the doctor whenever she gets paged. The range need only cover 50 feet radius (through office walls). This set of device need not be designed specifically for medical use. A restaurant pager (for waiting customers) is almost ideal, except that she wants the transmitter to be small and wearable. There are commercial "nurse call" pagers, but those are for multiple doctors/nurses and are overkill for this friend. Any ideas?